Why EDID is not trustworthy for DPI

Adam Williamson awilliam at redhat.com
Wed Oct 5 19:49:39 UTC 2011

On Wed, 2011-10-05 at 15:44 -0400, Simo Sorce wrote:
> On Wed, 2011-10-05 at 12:31 -0700, Adam Williamson wrote:
> > On Wed, 2011-10-05 at 18:49 +0100, Matthew Garrett wrote:
> > 
> > > So, ok, now you have some belief about the DPI. But which DPI? If you're 
> > > dual head, you've got two. Unless they match you're screwed - there's no 
> > > magic way to get applications to reflow text just because you've moved 
> > > the window between screens, and what would you do with a window that's 
> > > halfway between? You can argue that this is a corner case and obviously 
> > > yes it's a corner case but if you can't even pretend to fix the corner 
> > > case then your solution isn't a solution any more than 96dpi is.
> > 
> > There's no _magic_ way to fix anything, no. Things get fixed by code
> > writers writing code. That would seem to be the obvious thing to do...
> > 
> > Like I replied to ajax, I suspect when the problem of assuming
> > everything's 96dpi becomes simply too acute, instead of fixing
> > everything really properly so that all displays correct report their
> > size and all desktops actually do resolution independence perfectly so
> > it doesn't _matter_ if one of your displays is 98dpi and the other is
> > 215dpi, everything still looks perfect, the industry will just wind up
> > with a slightly more sophisticated bodge where we have a few 'standard'
> > resolutions and just figure out which one your displays are closest to.
> > But that's still going to require some kind of sensible handling of the
> > case where one monitor is roughly 100dpi and the other is roughly
> > 200dpi, unless we simply say 'you can't do that, all your displays have
> > to be in the same DPI Category'.
> Are you saying fonts should change on the fly when I move an app between
> 2 monitors that have different DPIs ?

If they're sufficiently different in DPI, sure. Or would you really want
everything to suddenly become twice as small if you were moving a window
from a 100dpi monitor to a 200dpi one?
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Twitter: AdamW_Fedora | identi.ca: adamwfedora

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